Reason behind software defect

when we think about what might go wrong we have to consider defect and failure arising from:
below are some sources mentioned  from where detect may come

1. Error  the specification design and implementation of the software system
2. error in the use of system
3. environmental conditions
4. intentional damage

now have look in above picture requirement number 1. Here you can see that requirements are correct , design is a correct build is also deployed correct and finally the product is working as expected to the requirement.so here there is no defect found due to each and every step is working fine. Now have a look on requirement number 2 in same picture you can find that there is a mistake made in build and due to which product is not working fine so defect found in production also. Now look into the requirement no 3 same picture here you can see that mistake is made im design due to which build meet the design which is not correct and hence the product is not working fine.

now have a look in requirement 4 here mistake is made in requirement due to which the design goes wrong due to which build meet the design which is wrong and hence the wrong product delivered

in all about 4 requirements you can see that reasons behind the defects can be anything. so it's very important while creating requirements, design , buipd ,, product that we are creating them correct