I really hate it when I have to guess stuff. This applies to CTFs, but also to my real-world work in penetration testing. It is incredibly frustrating to bruteforce or guess something, that could just be read in the source code. I much rather focus on technical details, tricks and techniques.
Try the XSS challenge: https://hacking.app/xss/xss_chall1.html#welcome
Failed DOM Clobbering Research part 1/2: https://www.youtube.com/watch?v=dZXaQKEE3A8
Chaining Script Gadgets to Full XSS part 2/2: https://www.youtube.com/watch?v=UGtrpXk6QVU