Grid trading, at its core, is a mechanical way to "make a living off volatility." You pick an ETF that swings up and down but doesn't really go anywhere over the long run, then you draw a sheet of grid lines over its price: every time it drops one cell, you buy a tranche; every time it climbs one cell, you sell one. Dips stockpile shares for you, rallies lock in profits — what you're harvesting is the back-and-forth spread in between.
It's happiest in a sideways market. Price gets stuck grinding inside a range, you buy low and sell high on repeat, scooping up the loose change others dropped in front of the vending machine — pretty effortless. But a lot of people blow up their first grid in a trending market: if price slides one way, your grid fills up fast, and when it keeps falling you've got no cash left to catch it — the account goes red all the way down. If price rockets up, you sold out early and watch it fly off without you, left holding nothing but regret.
So a grid is no "sit-back-and-get-rich" machine. It actually forces you to make two calls first: one, that this instrument will probably move sideways rather than plunge or moon; two, that you're willing — and able — to catch some falling knives with part of your capital. Bottom line: a grid earns volatility's money, not trend's. If you believe in the long-term climb, dollar-cost averaging probably fits your temper better; a grid only earns its keep when you're convinced the market is just going to grind.