Even if you have devoted a lot of time and effort to some project, if you know now that it is better to cancel it, do so. The fact that you have invested much energy is irrelevant. Deal only with the question: "Is this the right thing to do now?"

It is illogical to continue something just because you already started it. The matter has to be worthwhile in its own right. What was invested in the past is already over with, and need not tie you down to wasteful activities.