Tickets are the mechanism by which PoS works. You buy tickets which allow you to vote when your ticket is included in a block, and then also get some bonus DCR when you vote.
So at times it can be unprofitable to stake ? If the ticket price is too high? ...still trying to learn all of this.
If you are worried that you may actually lose coins because the price is too high then no. Whatever the price is, you get it back along with the bonus.
They only way to lose is if the ticket does not stake. In that case you get the price back but no bonus and you lose the transaction fee for the ticket purchase.
There is another theoretical case but it is extreme. It might be that you pay a transaction fee higher than the stake bonus. But that can't happen unless you put the fee too high on purpose.
Some people put a very high fee to buy tickets when the price is very low. Its the only way because higher paying fees get purchased first. Even in that case, at most, the fee they pay is about half the ticket bonus and depending on the low price of the ticket (to allow you to buy more tickets by locking the same amount of coins) it may or may not be worth it.