This one is just me being a bit of weirdo and a matter of perception.
I knew that Rangers won 9 titles in a row at one point in Scotland, but I was never exactly sure when. More to the point I suppose it never really registered with me what that would mean for Celtic players.
Was just looking at the career stats of John Collins who was a good player in the PL in his later years, famously played for Monaco for a couple of seasons and as far as I know is held in high regard at Celtic and is a bit of an icon. He only won one trophy in 6 years there, the Scottish Cup. Just seems odd to me an in a way that someone good, and who is very possibly better than anyone they have now won so little. Suppose them winning everything these days might have warped my perception. I'd have guessed that he would have at least 2 each of league titles, Scottish FA cups and league cups.
Edit: And now to completely trash the things I assumed about Scottish football in that same sort of period, Celtic weren't even runners-up for a number of years. I always thought the Old Firm established total dominance, finishing 1-2 once Fergie came to United but nope. Celtic finishing 5th? Wtf?
Celtic:
88/89 - 3rd
89/90 - 5th
90/91 - 3rd
91/92 - 3rd
92/93 - 3rd
93/94 - 4th
94/95 - 4th
Aberdeen 5 times, Hearts and Motherwell once each were runners up those years.