I trade off the order book and depth chart on gdax. I bought when I did because I saw the wall on the depth chart and was confident the price was going to upswing when it hit the wall. There were more buy orders than sell orders at that second. I stuck with my strategy however It didn't work that time. I'm not worried about losing money. I never sell below the price I bought in at. I just wait for it to come back up. Then place my sell order within a few dollars of the wall so I get the execution right before it hits and changes direction.
from your comments I couldn't figure out what coin you are trading. is it bitcoin?
generally speaking these walls are not exactly always the best source for any kind of analysis because sometimes they are there for manipulation and are placed by whales and will move if price gets near them.
with that said, buying something that is dropping is not always the best choice. for example altcoins are currently dropping but they are not going to recover for a very long time if at all for some of them.
and bitcoin is currently not going to have any major rallies and will continue to stay at this current price for a longer time.