We are often told, in one way or another, that things as they are, are not good enough. We usually grow up learning from people who do not yet feel satisfied, and they directly or indirectly pass on the idea that you or your life are missing something, that something is not yet complete, or there is more still to be achieved. And of course before this next thing comes, you can not relax. You must be tense, worried, perhaps even struggling until this next thing can release you, so that you may be happy.
And that is a huge reason for general discontent. Because we have been so conditioned to think that life is against us, and that now is not enough.
Nothing is secure. Everything that can be seen is subject to change. If that is contemplated, then the idea of final, absolute security at some later point is seen as an impossibility, and you are more free to enjoy life, act as you feel, but not waste your time waiting for the day when you can stop worrying about things. You don't have to wait for that.