Tension

There's a funny thing that happens to beginner musicians, singers, runners, and just about everyone doing something physical: they tense up. Runners tense their fists, guitarists their forearms, singers their throats and so on. It's like a reaction to being slightly out of your depth: you overcompensate by trying to add more power the only way you know how. Of course, all that extra power is just your muscles fighting themselves, and an important part of getting better is learning how to stop doing it.

I think there's an analogue in psychological tension too: when we have a difficult thing to do, it's easy to add extra unnecessary difficulty to it and make it seem bigger than it is. I sometimes pick up an old project that I abandoned and feel a sense of guilt that I didn't see it through the first time. Of course, that guilt is nothing but another kind of tension: your thoughts fighting themselves.

Ideally, you want each thing you do to take only as much energy as it actually needs. Anything extra is just inefficient.