Do you really want it?

Of course you would like to own the domain. That's why you placed your bid.

What are you going to do, if you can't get it? What if someone is always bidding higher and outbidding you? That someone might not even be human.

A bid robot might be what you up against, a 'machine' that bids higher, immediately and every time when you or someone else has placed a bid. This happens and speeds up often in the very last seconds of an auction leaving lower bids behind.
To protect yourself against such hi-tech bid wars and to protect you from bidding over and above of what you initially were willing to pay, decide before placing your first bid how high you want to go. 
Due to high popularity and other factors a top level domain might increase in price very rapidly during an auction. Setting your top amount, i.e. what you willing to pay, right from the beginning gives you a better chance to win the auction, meaning you are not being outbid by a 'bot' or another buyer.

In the last seconds of an auction, even during the very last second, things might happen so fast, that the domain you have set your mind on get snatched.

By placing the highest possible amount on the outset, your money is protected, because a bid can only go up so much each time as explained below.
At sedo a current domain auction price of $100.00 will increase by only $10.00 each time, when a higher bid is made. Once the domain is bid up to $500.00, the increase is $50.00 each time - and a domain auction having been bid up to $2.500.00 will increase by $100.00 increment, until the domain reaches $10.000.00.
By ordering an upper limit for 'your' domain, right from the outset, your buying intentions are protected, you are not prematurely priced out of the auction and you have excellent changes to win the domain. 

That is, if you really want it.