The variety of crystal forms that may be associated with one specific molecule of interest can be extremely large: in addition to polymorphs, all sorts of crystalline solids can be obtained, from molecular and ionic co-crystals to hydrates/solvates, to, needless to say, polymorphs of all these new crystal forms. Lack of predictability of crystallization experiments, far from representing a failure or a nuisance, should encourage in the crystal maker the same attitude shown by the three princes of Serendip (who were making unexpected discoveries by virtue of their "sagacity and readiness of mind") to be ready to pick new avenues as the crystal experiments will yield something unplanned for.
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