What are possible sources of error( errors that cant be corrected) for dna isolation and gel electrophoresis

what are possible sources of error that can occur. Sources of error are errors that occur that cannot be fixed. Anything that can be corrected is not a source of error. wat are the sources of error that can occur during gel electrophoresis, dna isolation and the PCR cycle.

Gel electrophoresis can be inaccurate if the DNA is supercoiled (causing it to run differently than linear DNA) or if the salt in the buffer is too high.

The biggest potential problem with PCR is nonspecific products. These occur when the primer being used recognizes a sequence other than the desired sequence.

ermmm would the dna be if a skin cell was to fall in to the source ??