I sometimes contemplate undertaking a major project. When I do so, I tend to end up reasoning like this:

It would be very good if I could finish this project. However, almost all the benefits of attempting the project will accrue when it's finished. (For example, a half-written computer game doesn't run at all, one semester's study of a foreign language won't let me read untranslated literature, an almost-graduated student doesn't have a degree, and so on.) Undertaking this project will require a lot of time and effort spent on activities that aren't enjoyable for their own sake, and there's a good chance I'll get frustrated and give up before actually completing the project. So it would be better not to bother; the benefits of successfully completing the project seem unlikely to be large enough to justify the delay and risk involved.

As a result, I find myself almost never attempting a project of any kind that involves effort and will take longer than a few days, but I don't want to live my life having done nothing, though. Advice?