“Doubt burns up everything, including the doubter.
To banish it bow down to the Lord.”
– T Krishnamacharya’s commentary to Yoga Sūtra Chapter One verse 5

“Saṃśaya (Doubt) is the Fire that consumes Wisdom.”
– T Krishnamacharya commentary on Bhagavad Gītā Chapter Four verse 40

“Jñāna is like a sword to cut away Saṃśaya.”
– T Krishnamacharya on Bhagavad Gītā Chapter Four verse 41

“What good is the sword of wisdom,
to cut away the chains of doubt,
if the holder is too weak to bear it.”
– T Krishnamacharya on the Bhagavad Gītā Chapter 4 verse 42

“Doubts always arise.
There is no doubt about that!”
– TKV Desikachar Religiousness in Yoga
‘Antarāyāḥ, Obstacles to progress, Techniques to Overcome them’
Chapter Fourteen Page 208

“Another way the mind functions is called Vikṣipta.
We act but we have doubts;
distractions come about,
there are obstacles.
The set direction does not look right
and we don’t know what to do about it.”
– TKV Desikachar Religiousness in Yoga
‘The Way the Mind Functions and the Concept of Nirodha’
Chapter Eighteen Page 251