There are two planes in Dota - horizontal and vertical. There are spells that interact with these planes which is called "forced movement": Toss (Tiny), Spear (Mars), God's Rebuke (Mars), Earth Spike (Lion), Hook (Pudge) and other spells that move or toss heroes. All of them, in addition to moving the target, also have their own effects. For example, while the target is flying from the spear of Mars, it cannot do anything - consider it a stun mid-flight, and then upon landing it also receives an extra. stun when the target hits the wall. But if, at the moment of this forced movement, the same movement is imposed on the target, then the latter cancels out the effect of the first. In other words, if Mars throws a spear and then instantly uses God's Rebuke, the shield will "erase" the effect of the spear as it's also a forced movement spell. The shield does not have a stun, so the target will be able to use BKB (which happened recently in the qualifiers). Such Mars players are universal mediocrity who want to press buttons like a boss but as a result they ruin the game for themselves, asking: "HOW?". Overall, how is this knowledge useful? You can push a mid-air ally spamming BKB button with Forcestaff and he will be able to do it.