Why did I fail in my Nisayon?

Sometimes people have Nisyonos that they are not able to withstand, and they fail.  This seems to contradict the idea that we are never put in a Nisayon that we do not have the ability to withstand.  The answer to this contradiction is that sometimes we put ourselves into a situation, that we were not meant to be in.  In that case Hashem has not given us the ability to withstand the Nisayon.

Another reason is that we can choose to fail.  Even though we have the ability to pass, we can choose to fail.

from a Shiur by Rabbi Noson Weisz about Beshalach from Aish Audio