You can't bid against yourself (unless you use multiple accounts to do so) since only one bid per bidder can count towards determining the price (which is based primarily on the highest bid of the second highest bidder, secondarily on the seller's minimum Starting or Reserve Price, and only slightly on the amount of the highest bidder's bid). There are two circumstances where placing a new bid while you are the current high bidder can cause the "current bid" to go up immediately. In neither case are you bidding against yourself:
1. If it is "Reserve not met" and the new bid is high enough to meet the reserve, the current bid goes up to the exact amount of the Reserve Price without need of another bidder. You are not bidding against yourself, you are bidding against the Reserve Price which you must meet to win.
2. If you are in the lead by less than a full increment (including having an earlier-placed tying amount) the current bid might go up to the full increment over the underbidder's maximum bid when you place a new bid. You are not bidding against yourself, you are bidding against the underbidder (the question being WHICH of your bids is used in calculating the price) and the general rule is that the price is 1 increment more than the underbidder's maximum bid. Then if there are no new bids by anyone except you before the end, the price might go down to the amount of the earlier bid after the end. This is a long story that has to do with a class action suit about a decade ago.
