Tacit knowledge is the lowest rung of understanding. It's the understanding that cats and dogs form, unable to talk but able to listen and consider. The main difficulty is that, because one cannot express tacit knowledge, one cannot reform or improve it.
Part of why operationalization is so important in the hard sciences is because it gives us access to otherwise-inacessible things, including tacit knowledge. The only knowledge that is tacit for the typical person is the knowledge of how to move muscles. For example, to whistle, the tacit portion is the pursing of the lips, but the rest of it is music theory which can be communicated and taught using language.
Part of why operationalization is so important in the hard sciences is because it gives us access to otherwise-inacessible things, including tacit knowledge. The only knowledge that is tacit for the typical person is the knowledge of how to move muscles. For example, to whistle, the tacit portion is the pursing of the lips, but the rest of it is music theory which can be communicated and taught using language.