I was Open Water Certified by YMCA, and the Instuctor was the best. The instructor gave me a lot of confidence. Also the course took a life time to complete, if I recall it took six weekends. One weekend was just dedicated to Skin Diving.
On one of the first dives after getting my open water cert. I had a equipment failure after a few minutes into the dive, instead of aborting the dive I was able to resolve the problem at the bottom (60 ft), doft and don my BC, fixed the BC strap that broke, and continued my dive.
Note the BC was a rental, and the plastic buckle broke. I had to tie the strap on the BC to fix the problem. Since I just started my dive I knew I had plenty of air, the vis was great, and the water was still.
After that problem, i've never rented another piece of equipment except for tanks.