B) we've gotten so used to working for a client that we cannot properly put ourselves into the position of client;
C) the grass is just always greener on the other side - our clients' projects are somehow more worthy and deserving.
People working in a creative industry have other traps that we fall into also. Attempting perfection is one of them, and another is that we don't necessarily want to have to look at our work (or perceived imperfections in our work) daily at home too. There have been numerous famous artists who have refused to hang their own art in their own homes. Or, as in the situation in my own kitchen, I see now that there are a few little things I should have done differently -- would never have done them this way had it been for someone else's kitchen (my house is, to some extent, my experimenting space) -- and changing it now would involve dismantling the whole kitchen. Who in their right mind would take apart a 2 year old kitchen and spend a few thousand dollars to correct a minor annoyance??
People hire accountants, interior designers, fashion designers (even if just by purchasing ready-made clothing), house painters, real estate agents, and countless others not because we cannot do our own taxes, plan our own renovations projects, determine our style preferences for clothing, paint our walls, or even sell our own homes. We hire people to do these things so that we don't have to assume the responsibility of doing it ourselves, so that our time can be spent doing other things, and so that hopeful these things will get done with fewer hitches and glitches.