Riddle about What comes once in a year twice

 What comes once in a year twice in a month four times in a week and six times in a day

The answer is 

letter e 

Step-by-step breakdown of the riddle:

1. Analyzing the frequency of occurrences:  

   • Once in a year: The letter 'e' appears once in the word year.  
   • Twice in a month: The letter 'e' appears twice in the word month.  
   • Four times in a week: The letter 'e' appears four times in the word week.  
   • Six times in a day: The letter 'e' appears six times in the phrase every day, if you consider reference to repetition.

2. Identifying the answer:
   The answer to the riddle is the letter 'e'.

3. Understanding why riddles are structured this way:
   Riddles often challenge us to think outside of normal reasoning. Here, instead of focusing on numbers or time, it cleverly directs our attention to language and the construction of words, showcasing the intricacies of the English language.