Part of my job as a teacher is to challenge students to help them develop. To do that, the challenge needs to be both reachable and a stretch. The usual way to do that is to put obstacles in their path, and keep it reachable.
I had a martial arts student who was coordinated, fast, and strong. To challenge him, I needed to stop or block techniques that could be done better. Because of my greater experience, I could do this though he was stronger and faster. But only if his execution was weak. He needed to fail occassionally.
About the same time, I had a woman student who was used to losing. Too used to it. To challenge her required having her win often in an honest fashion. Winning was a challenge for her. With practice, she was able to overcome increasingly challenging situations. The challenges were a stretch and reachable, barely.
Too often teachers present all students with the first type of challenge. Are your challenges to yourself and others both reachable and a stretch?