The ignorance is a creation of the Divine Maya, which operates in two ways, vidyamayi or a force of knowledge and oneness, and avidyamayi, a force of ignorance. The soul is a portion of the Divine that has accepted to enter the fields of ignorance so that it can grow from its seed state to a fully developed divine being. Pleasure and pain are incidents and processes for this initial first phase of its development. Once fully developed then it experiences not earthly joys which is a very diminished and distorted mixture but Divine Bliss. The soul instinctively knows it and hence is not only seeking this but is unhappy when our ego self is enjoying the mud and mire of earth and satisfied with it.
How does one know it? Well if we find the soul and even grow a little into its consciousness we shall know and not before that.
Affectionately,
Alok Da