Hope
Frostpunk invites you to lead the last city on the planet, so more often than not, you will need to make tough decisions that will negatively affect citizens.
So, to start with, here is a short list of all the ways:
Don't choose laws that diminish hope. Also, don't let the generator shut down to keep the whole city from freezing.
Discontent
It will only grow as you are generally adversely affecting. Here are some things to help reduce it:
By the way, some scenarios will purposefully increase the level of discontent. But, fortunately, they will also have ways to quickly reduce it.