To add liquidity and either miss the killer moves OR get the trade you don't really want
or to take liquidity and suck up the lost penny(s).
that is the unlubricated HTF question.
if they believe in your direction, they screw you with frontrunning sub-pennies or if they don't, may take the other side or just let your order run.
where they really cornhole your execution is with all market orders, like if you put in an order to go long 5000 shares with the last price at 15.52. say there are orders on the book to sell 2000 at 15.54, 1500 at 15.57, 1500 at 15.58 and 5000 at 15.60. the exchange "flashes" them your order and they just buy the aggregate 5000 at 15.54, .56 and .58 and sell it back to you at 15.60 all done in 7 billionths of a second. from there, you say to yourself, "damn, must have pulled the offers due to my chunky order" but if you look at the time and sales, you will see exactly why there are tiny droplets of blood in your boxers.
as such, latency of your connection is most likely not the problem. if the exchange holds your order for even 1/100th of a second(can be up to half a second), there can be 10 million nanosecond orders done.
pardon my scat hole analogy but it feels like a total psychological violation and i have all but given up adding liquidity with most of my strats because of this and have totally given up what was once a fairly profitable scalping strat.
it is happening to all of us, a penny or two here and a more costly missed opportunity there. dissect the enemy with the precision of a neurosurgeon and know exactly what keeps its heart beating.
william s. burroughs quote, "sometimes paranoia is just having all the facts."
