Think of skill ranks like this. I'll use swordfighting as an example.
0: Untrained. It's safe to say you don't know what you're doing. You learned your swordfighting skills from Hollywood action movies and Game of Thrones. Any remotely competent adversary would stab you to death with your own sword.
1: Familiar. You've read one or two books on swordfighting or had a fencing class and you know basic stances and simple maneuvers that would give you an edge over the average Joe. You can handle a sword without hurting yourself.
2: Knowledgeable. You know about swords and are beginning to appreciate the fact that an arming sword is not a broadsword is not a bastard sword. Reading the D&D books makes you giggle at the Arms and Armor section. You can handle swords with competence. You may be a re-enactor or an SCA member.
3: Experienced. You know swords. You've read manuals on swordfighting and can name and use several different styles and techniques. You have developed a natural feel for swords and can use even an unfamiliar blade with competence. If you were back in the Middle Ages you'd be a highly-valued man-at-arms.
4: Master. You're living in the wrong century. SCA members fear getting put against you in battle because you never seem to lose. You can quote the old masters of swordfighting and are familiar with almost every school and technique. The type of blade you're using no longer matters. In the Middle Ages, you'd be a well-known knight.
5: Legend. You can recite manuals of arms in your sleep. You can easily defeat a half-dozen people at once with a butter knife. You once performed an emergency appendectomy with a cavalry sabre and impressed even the EMTs. If you lived in the Middle Ages, you'd be a king's champion, if not the king himself.
Now ask yourself how many skills one could reasonably reach that fifth level in during a lifetime.
