Ridge (circle): The boundary is curved everywhere. The ellipses almost never touch on an axis — they land on the arc, so both β₁ and β₂ remain nonzero.
LASSO (diamond): The four corners sit exactly on the axes. The inner ellipse hits a corner first whenever the OLS estimate is off-axis — forcing one coefficient to exactly zero.
One word changes squared → absolute. One word creates sparsity.