"Like the Sun" is the title of a short story written by R. K. Narayan. It follows the story of Sekhar, a teacher, who decides one day that from now on, he will only ever speak the truth, rather than being polite and saying what people want him to say.
In order to help you answer your question with regard to the title of the story, I would first like to point out that it the title "Like the Sun" is actually mentioned straight away in the first line of the short story: "Truth, Sekhar reflected, is like the sun." You could argue that this makes the title very important, as this repetition of the title in the opening line creates a lot of emphasis on the title. Using the sun in a simile in this way shows the reader that the sun and the truth have a lot in common, which we can see as the story develops.
The sun is vital for our planet, as plants need it in order to grow and humans need the sun in order to survive. Likewise, the truth could be seen as vital to our interhuman relations. If we are honest with each other, life could be much better and we could all grow and develop much more, as we have nothing to fear if we always know where we stand and if there are no lies.
Another interpretation could be that just as the sun brings light to humans, the truth also brings light to human relations, as being truthful with each other greatly enhances our relationships by creating an atmosphere of mutual trust.
Lastly, in relation to the end of the story, you could go as far as saying that the truth can sometimes be harmful, just like the sun. If you are in the sun for too long, your skin can burn and it can even lead to skin cancer. Likewise, if you are not careful with speaking the truth, sometimes speaking the truth can hurt you, too. We can see this at the end of the story, when Shekar is told to finish the marking of his school work sooner than expected, as a direct consequence for having given his honest opinion to his boss.