That "90% memory used" number that made you order more RAM? It is almost certainly fine. Here is the metric that actually matters — and how to read it in under a minute.
Your laptop is warm and the battery is draining fast, but you are not doing anything. Here is what is actually happening in the background, and how to find the process responsible.
Your Mac slows to a crawl mid-task, then quietly recovers. It is not random — it is thermal throttling. Here is what it is, how to spot it yourself, and how to catch it before it bites.
Your fans are screaming, the palmrest is warm, and Activity Monitor shows a wall of numbers — but nothing obviously wrong. Here is what is actually happening, how to read it, and why thermal throttling is doing exactly what it should.