I'm going with the most obvious (Or second most obvious) with Jeff. How many times was he given the ball and how many times did he drop it? Left back in '03 when I was a come and go sorta guy so didn't get a chance to see his stuff but knew who he was upon his re-debut in '06 but looked up why he left and read on forums and so on. Then there's his suspensions, first time, please correct me if I'm wrong, was in '07 I believe, he was gone for a while and at that time I wasn't that big on reading stuff on the 'net like I am today so didn't know why he went, then there's '08, arguably on a huge roll, IC Champ, just defeated Triple H but came up short against Orton only to earn a shot at MITB only to get suspended again. Rumours stated he was going to win MITB as well. Then he was a good boy for a year or so before feeling burnt out and decided to leave. Ton of rumours circulated about a WWE return but nothing came of it so he returned to TNA because of the way Punk spoke on him in his Breaking Point promo, days after his drug charges began and to this day the case is still on-going. Had he not had so many drug problems, he could've been the face of the company. The guys what, 32/33, about the same age as Cena, so could've had more feuds with more guys (HBK vs. Jeff would've been great at WrestleMania), maybes a Rumble win and become a top star of the decade, yet he was only really a top star for about two years, now he's let himself go a lot and from what I've heard he's changed in the ring as well (Since I don't watch TNA myself)
Another one is Mr. Anderson, he was on fire in '07 but the fire was put out when he was injured during his MITB run which Edge capitalized on, won the briefcase and a day later cashed it in on 'Taker to win his first of 5 World Titles, a spot that was reserved for Kennedy. But then he was set to be named the son of Vince, but a suspension cut his push short and we all know how that storyline turned out, and he didn't seem to do much after that, had a feud with HBK, but after that nothing that memorable. I think, had he not been suspended that he would've had a huge push, being named the son of VKM, possibilites are endless, or at least were endless.