Ok, heres how it is,....
An old...weathered.... well stuck sticker doesn't really let anything get under it to melt the glue. All you're doing is attacking the very edges, and slowly picking away at it,....ane eventually it can be removed using all that junk that has been mentioned, that really is much better at removing the glue after the sticker has been removed,....not before

Now then,....those of us that have told the proper.....proffessional way of removing a sticker,.....namely using a heat gun, do know what we're talking about. If you don't believe us, ask the proffessionals that do it all the time !

Now, it should be well known that if its a relativly new sticker that has not been sun beaten and froze to death, it may be removed w/o much trouble using nothing but fingernails, and then w-D