Frustration

Sure this has been discussed numerous times.....But how do you push past the frustration when building a car? Things are going good, as far as I am concerned. But I sit here and can't help but think if I might have made a mistake taking on my project. I think about all the $$$ in it so far and all the $$$ it is going to take to complete it. Not to mention all the time it is going to take to finish when it comes back. Couple that with my body slowly falling apart at the ripe old age of 44 and it really has me wondering......