The upper picture shows a small planet and the red arrows show the gravitational forces attracting it towards a much larger planet off to the right. Since gravity is proportional to 1/R^2, the forces to the right are slightly larger than those at the center, which are slightly larger than those at the left.
The lower picture shows the forces when a constant offset corresponding to the force at the center has been subtracted from all forces. The central force is then, of course, zero. A small force remains towards the right, directed rightwards. A small force, directed leftwards, remains at the left. This is why (perhaps somewhat counter-intuitively) tidal forces lead to a bulge on both sides of the smaller planet.
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