PPE every time
Goggles and gloves, ventilation, and never water into lye.
Usually the fragrance oil, occasionally the temperature, never bad luck.
Soap making is chemistry with a small margin. Running every recipe through a calculator takes two minutes and prevents lye-heavy bars, and knowing which fragrances accelerate prevents most ruined batches.
Candles are pure testing. The wick chart is a starting point, not an answer, and the only way to know a combination works is to burn it repeatedly and write down what happened.
Both reward records. Makers who log every batch improve steadily; makers who rely on memory repeat the same faults and never work out why.
Goggles and gloves, ventilation, and never water into lye.
The log is what turns accidents into knowledge.
Burn tests and labels come before money changes hands.
Twenty minutes, free, on your setup, your recipe and what to make first.