It’s a reminder of dead branches in a tree trunk.
A natural thing. When processed and managed, it is a would-be imperfection that could be nice to look at, causing a waving grain, adjusted in directions exploited by purpose. It is decorative and agile in its language, but still a defect.

A flaw to the strength of wood, it leads to weakness for tensile and compression, especially when under perpendicular forces or being pulled in opposition. This would be structurally unsound to build upon. The knot can lead to cracks and would not be of benefit in building because of the warp, the check and the shakes.

Some who construct would know the impact.
In a dissonant chord, it is the note that sings loudest and rings a disjointed sound.
In a poem, it is the missing iamb of a sonnet, tripped and stumbled upon. In a house, it is in the failing wall or a cracking joist, unable to stand the weight of heavy burden.
In speaking-it is missing a word and rushing over – leaving a hole. Such work is helpless and unsound.

What remains would not be usable.