As it is true that guru enlightens the student with knowledge, Sage Patanjali takes great pain to make sure we do not underestimate the power of obstacles on the path to acquiring knowledge. He enumerates them and then warns us of their debilitating consequences on the body and mind. At first he mentions sickness, meaning attention must be given to right diet and a proper lifestyle ensuring a healthy body and mind. Followed by mental indolence, doubts, lack of determination, laziness, craving for sense pleasures, delusions, despair arising from a deficit in expected, or meagre results, fluctuating concentration, etc. With a healthy body the mind is easier to control and kept awake. If the mind is allowed to become slothful the body is surely affected, and soon becomes vulnerable to illness. Doubts arise from ignorance, and can be squashed only with right arguments based on realised knowledge.
Determination comes from conviction in our undertaking, thus a deficiency in our resolution arises out of not properly understanding the aim and objective of our endeavour. Laziness is symptomatic of tamas, ignorance, disregard for the value of time and energy. The endeavour to gratify the sensual urges is a losing game. If anything is insatiable its surely sensual craving. Unable to satisfy the senses we become frustrated with ourselves, and this spills over to our dealings with near and dear ones, threatening even our steady relationships. Thus such recurring disappointments burdens the mind.
Delusions are flights of fancy mostly to escape the humdrum of repeated practise, occurring because of not having discovered the innovativeness and versatility of the mind that can add colour and variety to apparently tedious tasks. The opposite of despairing is having patience when results of efforts are not forthcoming. When the mind is earnestly applied in learning a subject then commensurate result is sure to follow, this is the unfailing rule of nature which one need not be sceptical about. In this regard self doubt alone plays spoil sport.