this is bs, there are percentages, and you can calculate aproximatively how long should it take to catch a specific pokemon or achieve another task, if it was 1 chance out of 1,000,000,000 and you can have 1 opportunity every minute, of course you could be lucky and catch one in a single day, but math says you will likely need about 30 years of continuos gameplay to catch it (these numbers are just an example).
if you can't understand math behind what you call luck, you should play lottery, not pokemmo (even if sometimes they feel the same thing)