For years my approach to a misbehaving I2C device was to stare at the datasheet, re-read my code, and swap wires until it worked or I gave up. It is an embarrassing way to debug something that is, at heart, just edges on two lines.
This week I finally bought one of those clone logic analysers, the little blue board that pretends to be a Saleae and costs about twelve quid. Plugged it into the SDA and SCL lines, fired up PulseView, and there it was. The whole conversation, decoded. Start condition, address, the read bit, the ack, the bytes, the stop. No guessing.
My sensor was not answering because I had the address wrong by one bit, which I would have sworn blind I had not. The analyser did not argue. It just showed a NAK where I expected data, and a NAK means nobody at that address is listening. Two minutes to see, after about three evenings of theorising.
The real shift is mental. The bus used to be an abstraction I held in my head and hoped matched reality. Now it is a trace I can look at. I should have bought one years ago, and if you are still poking at I2C or SPI by inference, buy one this week.