Project details are the hooks keep knowledge in your brain.
Specificity matters."I want to be able to order coffee in Paris and have a chat with my server," helps more than "I want to learn French." The former tells you what vocabulary to learn, allows you to visualize the end, and makes your motivation tangible. "I want to create a command line alarm application" beats "I want to learn Perl" every time.
Find a problem that you want to solve. A childhood dream. A minor annoyance. Learn enough to solve it. Pick again.