Few words carry as much contradiction as the ones in this short piece about thinking. The speaker begins by simply listing what thoughts can be: dangerous, beautiful, able to make you forget or remember. Nothing is settled at first. Thoughts seem to cut both ways, and the short, flat lines make them sound like a fact the speaker has learned the hard way.
The ending makes it personal. Thinking helped the speaker forget their pain, perhaps by drifting into something else, but the same drifting led straight back to it. The single word "but" sits alone on its own line, like a pause before a drop. After it, "once more" suggests this has happened before and may happen again.
The mood is quiet, tired, and a little trapped. The poem never says what the pain is, which leaves it open and lets any reader fill in their own. What comes through is the feeling that the mind is not easy to control, even when you are trying to escape something.