Sometimes, people have life problems that can be entirely solved by doing one thing. (doing X made my life 0.1% better, PERMANENTLY!) These are not things like "This TAP made me exercise more frequently", but rather like "moving my scale into my doorway made me weigh myself more, causing me to exercise more frequently" - a one-shot solution that makes a reasonable amount of progress in solving a problem.
I've found that I've had a couple of life problems that I couldn't solve because I didn't know what the solution was, not because it was hard to solve - once I thought of the solution, implementation was not that difficult. I'm looking to collect various one-shot solutions to problems to expand my solution space, as well as potentially find solutions to problems that I didn't realize I had.
Please only put one problem-solution pair per answer.
Signing up for email from Superhuman. I went from "always have a pile of unchecked email, very bad responsiveness, feeling of overwhelm" to "I look forward to checking my email and inbox zero everyday effortlessly".
The change happened basically immediately after the 1h onboarding session.
This was actually a major update in how building software to reduce frictions can cause qualitative changes to my productivity.
I could rave about superhuman for a long time, enough that this answer will just sound like an ad. But take it upon my karma and reputation as an LW user that it's just my genuine opinion.
Inbox was awesome and I used it from day 0 to day day -1. Adding a note to the reminder when you snooze was the most useful part.