B J Fogg'dan

For somebody to do something – whether it’s buying a car, checking an email, or doing 20 press-ups – three things must happen at once. The person must want to do it, they must be able to, and they must be prompted to do it. A trigger – the prompt for the action – is effective only when the person is highly motivated, or the task is very easy. If the task is hard, people end up frustrated; if they’re not motivated, they get annoyed.