How likely is eye laser surgery going bad?

Slim but not zero: Most people end up much better after surgery than before without glasses, but the chances of having a complication are still there and real, probably less than 1%.

Low: Generally, lasik is very safe and the risk of vision loss is far less than 0.1%. Like most surgeries, the risk of bad results decreases as the surgeon's experience increases. You should ask how many procedures the doctor has performed, what his/her rate of complications is, and the percentage of patients with similar prescription who have achieved their target result. This info should be available.