Liquid compression is difficult but not impossible because they feature a mid-level intermolecular force that makes their molecules difficult to compress. Intermolecular force is the strength used to hold molecules tightly together or force them apart. The strength of the intermolecular force depends on the state of the matter, with solids having the strongest intermolecular force and gases having the weakest intermolecular force.
Compression of Water
The strength of its intermolecular bond relative to its thermal energy, or temperature, is a determining factor in liquid compression. Water, for example, compresses into solid ice with a strong intermolecular bond when its thermal energy reduces. That compression, however, is hard to maintain because ice melts quickly and resumes its non-compressed form as soon as its thermal energy increases a single degree above its compression (freezing) point.