This is a Heyacrazy puzzle.
Rules of Heyacrazy:
Shade some cells of the grid.
Shaded cells cannot be orthogonally adjacent; unshaded cells must be orthogonally connected.
When the puzzle is solved, you must not be able to draw a line segment that passes through two borders, and does not pass through any shaded cells or grid vertices.
For an example puzzle and its solution, see this question.
This puzzle is the most difficult Heyacrazy I have made. But it has a solution without "case-bashing" -- there is a clean logical path, one that does not involve any deep hypotheticals. Any sort of "what-if" logic should be very easy to do in your head, without ever marking any cells you are unsure of (even if only for the purpose of arriving at a contradiction).