How do you stay motivated and overcome procrastination when working on challenging tasks?

First, you have to know that procrastination is not laziness. It is a part of depression. Usually, because what you do seems useless. Unless you find a purpose, a value of this job, you will be suffering :( Don't start until you disassemble challenging tasks into atomic ready-to-get-done within 10 minutes tasks. Then, every micro-task done will push you forward. A big job can seem impossible to handle.

Try using IXORD Notes, you can distribute your tasks and at the same time you will understand how many tasks are left and the application can help you mentally.

the main and only challenge is starting a sitting down to do something any meaningful work is challenging, tough and scary. I rarely feel motivated to do it but using discipline (which I practice and develop daily in personal life) lets me get over the “start it” barrier. Also getting into a habit of doing a little something, creating any traction on key projects every day has been the game changer for me

Take a step back and meditate for 10-15 minutes to clear my mind and bring focus and clarity to the problem. Usually makes the task easier with a clear head. That and having a conversation with a colleague around to topic to get a new perspective for the challenge at hand.