I was asked the question “When should you tell the Truth?” and so this is my reply.

The Vedic culture had a wonderful perspective on this subject. They were totally focused on being always truthful because this is in all of our interests to be honest and truthful. Truth was seen as an integral part of becoming enlightened and dishonesty has the pernicious effect of covering people’s hearts and minds in ignorance and contributes to the material entanglement of the soul.

Yet truth should not be used as a cudgel to cause pain or injury to others. I shared a couple of very nice Vedic verses on this subject.
Austerity of speech consists in speaking words that are truthful, pleasing, beneficial, and not agitating to others, and also in regularly reciting Vedic literature. Bhagavad-gīta 17.15

satyaṃ brūyāt priyaṃ brūyānna brūyāt satyamapriyam | priyaṃ ca nānṛtaṃ brūyādeṣa dharmaḥ sanātanaḥ || 138 ||

He shall speak what is true; and he shall speak what is agreeable (pleasant); he shall not say what is true, but disagreeable; nor shall he say what is agreeable, but untrue; this is the eternal law.—(Manu Saṁhitā 4.138)

Truthfulness means to speak the truth in a pleasing way, as declared by great sages. Bhāgavata Purāṇa11.19.38

One of my spiritual teachers replied to this question in a most wonderful way: “Regarding your questions, your first question was should the transcendentalist always speak the truth to everyone in all circumstances? The answer is yes, one should always speak the truth, but a qualified devotee will be able to always speak the truth in a way that is very palatable to everyone – so that it will sound pleasing even to his enemy. That is the art of speaking truth. It is certainly so, that we must speak the truth to all people, but how you say it that is another thing.”