Are rules and theories of commerce irrational?

There are many rules and theories in commerce which have been made without giving any reason or sufficient reasons.

We have a rule in accounting in Real account that Debit what comes in and Credit what goes out. But, why it is that way and why not vice-versa has not been told.
However, debit is positive and credit is negative. I have found out the reason that why such rule is there because what comes in is added and what goes out is negative.

Another rule is accounting in Personal Accounting that Debit the receiver and Credit the giver is also existent in Accounting books without giving any reasons for the same.
However, I found out he reason without doing any extensive research but just using common sense. During Renaissance in Europe and initial stage of Capitalism, it made barter system obsolete and trading started mostly on the bases of credit to save time and other resources. Therefore, we can credit the goods account as it is going out but we cannot debit anything as cash is not received and goods are bought on credit. Therefore, this rule is made for double entry by debiting the debiting the account of purchaser and crediting goods (sales account).

Last rule is debit the expenses and credit the gains.
If what comes in is greater than what goes out then it is a profit while what going out is greater then it is a loss. This rule is as such because of filing the gap in double entry. It is a rule as such because at the end of the accounting year, we have to calculate profit and loss for every transaction incase of single entry and double entry saves time and effort by simultaneously recording profit and loss for every transaction. 

UPSC annual exams for the post of IAS/IPS/IRS etc.

The Union Public Service Commission (UPSC), a government body of India, situated at Shah Jahan Road near India Gate holds exams annually for the selection of the post of IAS/IPS/IRS etc.

Every year, about 9-10 lac candidates from all over India apply for the positions and a handful of about only 1000 candidates are selected after going through 3 stages of the selection procedure. First is a preliminary exam of multiple choice questions, second is Mains exam of subjective type questions, and finally the third stage is interview by which candidates are selected and then sent for training. After many months of training they are given the post of IAS/IPS or whatever they qualify for.

However, this is a very tough exam as I already mentioned that out of lacs of candidates, only a handful of them around 1000 are selected. After GaoKao exam in China which is the world's toughest exam UPSC ranks second in the list of world's toughest exams. The course of General Knowledge is so vast that many candidates, including me at one point of time got confused as to what should be learnt and understood and what should not be.

It has also caused distress and disappointment for candidates and some have even committed suicide due to their failure to clear the exam. In 2013, an aspirant doctored and forged documents to impress his family members and his friends in Facebook. However, he could not hide his failure for long and when he knew that truth will definitely come someday somehow, he committed suicide.

The solution to this according to me is that candidates should start preparation for UPSC exams from childhood itself as the General Knowledge course is very vast. They should also keep an option available like trying for State Civil Services if the Central Civil Services is not their cup of tea because the State Civil Services Exams are about 50% easier than Central Civil Services Exam.