Advancement in the enlisted ranks is something of a crap shoot. Picking the "right" rating may have more to do with one's promotion opportunity than quality of performance.
The probability of an enlisted Sailor advancing to the next paygrade during any given advancement cycle is unclear. Sailors trying to advance to the next paygrade often go blindly into an advancement examination without knowing the advancement cycle's quota. While job performance and advancement exam score play a big role in determining whether a Sailor advances or not, quotas determined by Naval Personnel Command can play a more significant role. Sailors often trust their luck that the advancement numbers for the cycle are favorable. Quotas vary greatly from cycle to cycle, while certain ratings have inherently greater advancement rates than others. Ultimately, this gives great advantages to some anil leaves others in more difficult advancement positions.