Question on stealth!

This is my first time as a rogue, Blood Elf, 29, every single time i go stealth around an Alliance player i get hit. It's like they can see me when i'm stealth, i just don't understand. This just happended twice again while i was questing in Ashenvale, i got engaged by a hunter, but i didn't notice him so i vanished so i could get away, but he still managed to kill me. And then i was heading towards the west side of Ashenvale when 2 paladins stopped i front of me (probably some friends) to decide if they engage me or not, we were like 10 meters away from each other, i immediately use stealth because i know i will get fuucked. I go around the road, thinking they will just give up and move on, but they went EXACTLY towards me and killed me in an instant, i was stealthed for a good 5 seconds and they still got me. Can someone help me on this? Like i just don't get it, i genuinely don't get it, i just don't fuucking get it, it's ALWAYS the same thing, i ALWAYS get caught. Stealth/Vanish is one of the most important things to fight as a rogue and it's so vulnerable, it's almost impossible to fight, i'm just not getting it. INB4 noob, scrub etc... I'm not hating on Rogue, i'm having a blast, it's just this stealth thing, i'm not getting it. Can someone be so kind a take a bit of their time to explain to me why i always get caught and how stealth works exactly? I mean i understand getting killed by hunters cause they have the mark and other debuffs when they engage, but most of the times i just go invisible for a good 5 seconds or more and Alliance players still get me.

Some classes/specs/races/items have increased stealth detection.
You are more likely to be spotted if you approach from front. Always creep up from behind.
Higher level players/mobs will spot you more easily, 80lvl player will just laugh as you "stealh" around, they just see you.
Any Dot's or any damage will break stealth, so if you Vanish while you have DoT on you(example - hunters sting) it will break.
Hunter's mark will make you visible to enemy, even if you are stealthed.

It's not impervious invisibility, there are rules.

Make sure you have highest rank of Stealth you can learn.
For successful stealth you need to put talents in it, especially in PvP.

This is exactly what i was looking for. Thank you! I feel more relaxed.
Nice pic btw