People describe it as weight because that is how it is experienced. The relief comes from the thing leaving you, not from anyone hearing it.
The phrase is old and unusually accurate. Unsaid things really are experienced in the body: a tightness across the chest, shallow breathing, a jaw you did not notice you were clenching. That is not a metaphor people invented, it is a description.
Which is a useful clue about the fix. The relief people describe does not come from being advised, or agreed with, or even understood. It comes from the thing moving from inside to outside.
None of these require the person it is about, and none require an audience.
The most common mistake is writing the presentable version. You make it balanced, you acknowledge their side, you soften the part where you sound petty or furious or pathetic. Then you notice you feel exactly the same afterwards.
That is because the pressure was in the unreasonable bit. Whatever you skipped is the thing that was sitting on your chest. Nobody is marking this. The version that helps is the one you would never say aloud.
If what you write is going to persist, some part of you writes for the future reader, even if that reader is only you in a year. That is enough to make you tidy it, and tidying is the thing that stops it working.
On drift you write it, it surfaces for a while, other people can mark that they felt the same, and then it goes. Out of you, and not sitting anywhere afterwards.
Generally yes, because it converts a vague, looping feeling into a specific thing with edges. The relief comes from expressing it rather than from being heard, which is why it works even with no audience.
Write it as though you were saying it to them, and do not send it. You get the release of having said the true thing without the consequences of a conversation you may not want or be safe to have.
Usually because the version you expressed was the edited one. If you left out the part that felt unreasonable or unkind, the pressure is still where it was. It can also mean the problem needs a decision rather than a release.
Say the version you would not say out loud.
Drift in →