I am having a very hard time understanding why there is no such button on Course Challenges, when it already exists practically everywhere else.

The way Course Challenges are created seems to be in direct opposition to how everything else in Khan Academy functions. 

You cannot restart the Challenge.

It actively PUNISHES YOU for skipping/trying to get it to end faster so that you can retry it by TAKING AWAY PROGRESS. Which could mean DESTROYING A PERFECT MASTERY SCORE. 

I expected more knowledge about human psychology from the creators here. This is how you lose people permanently unless they are forced to use your platform. Either punish mistakes in unit tests ALWAYS or NEVER punish mistakes in Course Challenges by TAKING AWAY PREVIOUS SUCCESS. 

I cannot even believe that this is a thing. Who decided it is a good idea to strip previous progress? And NOT MENTION IT at the start? BRIGHT RED ALL CAPS????