For me, I know my ability to learn whatever I need to in order to complete the project. Most of the time, a client will approach me and say "Can you do x, y, a

For me, I know my ability to learn whatever I need to in order to complete the project. Most of the time, a client will approach me and say "Can you do x, y, and z for this project?" While I can do x and y just fine, I know full well that I haven't the slightest idea about z -- but I still say "yes." I then do a little bit of research on the topic and get back to them with an estimate. I then have a strong motivation to learn 'z' to be able to complete the project and get paid, and will also have gained a valuable skill that I'll be able to leverage in the future.