If the person at whom it is aimed happens to be busy or already engaged in some definite train of thought, the particles of his mental body are already swinging at a certain determinate rate, and cannot for the moment be affected from without.

In that case the thought-form bides its time, hanging about its object until he is sufficiently at rest to permit its entrance; then it discharges itself upon him, and in the act ceases to exist.
The self-centred thought behaves in exactly the same way with regard to its generator, and discharges itself upon him when opportunity offers.

If it be an evil thought, he generally regards it as the suggestion of a tempting demon, whereas in truth he tempts himself.

Usually each definite thought creates a new thought-form; but if a thought-form of the same nature is already hovering round the thinker, under certain circumstances a new thought on the same subject, instead of creating a new form, coalesces with and strengthens, the old one, so that by long brooding over the same subject a man may sometimes create a thought-form of tremendous power.

If the thought be a wicked one, such a thought-form may become a veritable evil influence, lasting perhaps for many years, and having for a time all the appearance and powers of a real living entity.
All these which have been described are the ordinary unpremeditated thoughts of man.