Yama said:

The good is one thing; the pleasant, another. Both of these, serving different needs, bind a man. It goes well with him who, of the two, takes the good; but he who chooses the pleasant misses the end.

Both the good and the pleasant present themselves to a man. The calm soul examines them well and discriminates. Yea, he prefers the good to the pleasant; but the fool chooses the pleasant out of greed and avarice.

O Nachiketa,

after pondering well the pleasures that are or seem to he delightful, you have renounced them all. You have not taken the road abounding in wealth, where many men sink.

Wide apart and leading to different ends are these two: ignorance and what is known as Knowledge.

I regard you, O Nachiketa, to be one who desires Knowledge; for even many pleasures could not tempt you away.

Fools dwelling in darkness, but thinking themselves wise and erudite, go round and round, by various tortuous paths, like the blind led by the blind.

The Hereafter never reveals itself to a person devoid of discrimination, heedless and perplexed by the delusion of wealth. "This world alone exists," he thinks, "and there is no other." Again and again he comes under my sway.

Many there are who do not even hear of Atman; though hearing of Him, many do not comprehend. Wonderful is the expounder and rare the hearer; rare indeed is the experiencer of Atman taught by an able preceptor.

Atman, when taught by an inferior person, is not easily comprehended, because It is diversely regarded by disputants. But when It is taught by him who has become one with Atman, there can remain no more doubt about It. Atman is subtler than the subtlest and not to be known through argument.

This Knowledge cannot be attained by reasoning. Atman become easy of comprehension, O dearest, when taught by another. You have attained this Knowledge now. You are, indeed, a man of true resolve. May we always have an inquirer like you!

Katha Upanishad. Chapter II. Verses 1-9.

Source: "The Upanishads - A New Translation" by Swami Nikhilananda