The idiom to 'hit a wall' means to come to an obstacle or a mental barrier that is impossible to overcome or to get past. When you 'hit a wall' you are stuck at a particular point and find it hard to progress. To 'hit a wall' can also mean to become exhausted or so tired that you can not continue.

1. Halfway through the marathon, Helen hit a wall and could not go any further. She was completely exhausted!
2. I have hit a wall with my research for my thesis. I need to find a few more sources to consult.

1. We had gotten quite far with creating the new marketing strategy but now we seem to have hit a wall. I think we need to have a good brainstorming session and toss some ideas around.
2. I hit a bit of a wall with my work and had to ask Sarah to give me a hand. She is great at overcoming stumbling blocks.