If you have expectations, they can always be disappointed and they will. You are likely not to like what you see. If you don't expect, nothing can be disappointed. You might like everything, out of nowhere.
On your second visit you happen to like Bangkok, to embrace every part of it, while you had never wanted to go there again after your first. Reaching Nongkhai, which was colourfully painted out in your imagination, you happen to dislike it. You will leave for Laos tomorrow (which is a good idea anyway!).