Most of us have a problem with motivation. Effective Altruism suggests that we can do substantial good through acting altruistically. Yet, it is hard for an individual to motivate himself to act as well as reason requires.
Normative judgements and psychological motivation
A normative value judgement about how best to act is a separate matter from the psychological question of motivation. Effective Altruism answers the normative question of what to do but perhaps has given less attention to motivation.
Effective Altruism reasons from a perspective that values sentient welfare impartially and suggests that it is normatively good for individuals to make substantial donations to effective charities, be vegan and direct their careers towards the common good. We believe these actions are normatively good from the point of view of the universe as in expectation they improve aggregate welfare, but we struggle to act on this understanding.
Not many saints
Full-on altruism may be normatively good, but few are able to motivate themselves to meet this standard. There are some saints, but not many. For most people it is hard enough to care prudently for their future selves as with dieting and exercise, so that to go further and make big sacrifices for anonymous others is very difficult. A further challenge that effective altruists face is trying to live up to EA standards that are alien to the society around them.
Motivation can be improved by developing good habits, making commitments and being with like-minded people. Some effective altruists do great things but others are wracked with guilt for failing to do what they believe they should. And effective altruists are unusually committed compared to the general populations. There are limits to what we can expect from individual altruistic motivation.
Willpower is weak but social norms are strong
Lack of individual willpower is a human weakness but fortunately we have a compensating strength in our ability to follow social norms. People do good more reliably by following social norms than by independent supererogatory action. This is because social norms are backed by evolved reactive attitudes including resentment and shame, and are sometimes further supported by law. A norm-backed requirement such as not to steal is naturally followed, while to go beyond society's norms, as EA proposes with donations and veganism, is harder.
Importantly, it is improvements in norms and law rather than individual sacrifices that have given us moral progress and changed the world for the better.  Taxation and the welfare state have done more than charity to improve welfare.
Implications for effective altruism
Effective Altruism should work with a realistic theory of motivation. This should recognise that more reliable motivation comes from norm-following rather than from individual willpower. I suggest six implications from taking this perspective:
1. We should stop feeling so guilty. It is unnatural to make big sacrifices beyond conventional norms and we can't push ourselves too far.
2. Moralistic language should be avoided. We should reserve talk of ‘duty’ for a society’s core moral requirements, and instead frame donations as doing additional good.
3. Giving What We Can is right to build a donor community with donation norms and to support donors to make manageable commitments and build good habits. These approaches reduce the need for willpower and can make donating more enjoyable and more reliable.
4. We should not expect all effective altruists to be donors and vegans. We do not want to exclude people who give a lower priority to personal altruism but are instead focused on researching how to do the most good, or on implementing EA projects. This broad church approach may, though, cause tensions between different groups and may appear somewhat hypocritical.
5. We may have high hopes for growing philanthropy's scale and effectiveness, but should be realistic that charity is only a modest element within human affairs. It may be that even with Effective Altruism, the biggest impacts will not come from charity. I suspect EA will make its biggest contributions from developing and communicating its global priorities ideas such as around longtermism and animal welfare. It will also contribute by managing philanthropy well. Individual donations do very significant good, but they may ultimately be relatively less important.
6. In our thinking, we should keep separate the normative question of what it is good to do, and the psychological question of motivation. The normative answers we reach will probably be very demanding, which will leave the separate psychological challenge of how to motivate in the right direction. And this challenge will likely be mainly met not from individual willpower, but from changes in norms and law. 
The separation of normativity and motivation has been controversial. See Alvarez, Maria. 2017. “Reasons for Action: Justification, Motivation, Explanation.” The Stanford Encyclopedia of Philosophy. https://plato.stanford.edu/archives/win2017/entries/reasons-just-vs-exp. and Singer, Peter. 1981. The Expanding Circle: Ethics, Evolution and Moral Progress. 2nd Edition 2011, Afterword to 2011 Edition.
On evolved morality see Haidt, Jonathan. 2012. The Righteous Mind: Why Good People are Divided by Politics and Religion.
See Pinker, Steven. 2011. The Better Angels of Our Nature: Why Violence Has Declined.
Political theories need accurate views of human nature as argued in Singer, Peter. 1999. A Darwinian Left: Politics, Evolution and Cooperation.
My website and blog are mainly about philosophy and effective altruism http://jamesaitchison.co.uk. I am on Twitter @jdawelwyn.
I think this is right and is more true and important when the positive impacts you might have are distant in time, space or both. If you're doing something to help your local community then you should be able to see the impact yourself fairly quickly and willpower could well be the best thing to get you out picking litter or whatever. This falls down a bit if your beneficiaries are halfway round the world, in the future, or both.
Yes, it is harder to care for distant or statistical people even if it is normatively the right thing to do. We shouldn't overestimate how much we can do by will power alone, but changing norms may be effective.