Being a value investor doesn't mean you have to hold forever.
You CAN just hold until its reasonably valued. Admittedly you might leave between 40% and 150% on the table, typically, but if you exit you aren't taking the risk it wil sink back down, either.
To use the example above, I bought a large XOM position around $45 and exited around $60. At $45 it was silly-cheap and I was quite happy to walk away with $15 a share in profits. Ok, it went lots higher, and i missed that upside, but then again, I found another, MORE undervalued stock around that time, and have now doubled on it, since.