I like most people blame "the system" for much of the problems that we in the construction industry have to face on an almost daily basis. For example, some of us are lucky enough to go to school to learn stuff such that we might get a job and make a useful contribution to the business of our employer. That is "the system" and as a consequence almost all employees complete their timesheets on an hourly and daily basis such as to demonstrate that they have managed to achieve something of value to the benefit of their employer.
I have never yet seen a timesheet that contains the words: "Come to work, did absolutely nothing all day and then went home" because "the system" has programmed employees to demonstrate to their employer that they have been gainfully employed even if they have not. Indeed, failure by an employee to demonstrate gainful employment might effectively be Inviting dismissal and from there it simply follows that an employee's survival within "the system" positively encourages dishonesty.
It is therefore "the system" and the dishonesty that it encourages that has on occasions (to my certain knowledge) defeated claims for loss and expense that really ought to have been successful. You will no doubt have heard lawyers use phrases like "cause and effect" and "liability and quantum" and which, in very simple terms, means that it is for a Contractor to prove that the Employer has done (or has not done) something that it should not have done (or should have done) (and being the cause and liability bit) and which has directly resulted in the said Contractor suffering a damage / quantifiable loss [the effect and quantum bit].
It is however one thing for a Contractor to demonstrate that a failing of some sort on the part of the Employer has directly caused it to suffer a loss but quite another thing to prove the amount of that loss.
It is at that process of proving the amount of the loss that, more often than not, it all goes horribly wrong because the evidence on which the Contractor will frequently have to rely is the aforesaid timesheets that record that the entire workforce was gainfully employed when, in truth, it comprised a large (sometimes huge) number of men that achieved absolutely nothing at all but dare not admit it.
Having thus amassed reams of evidence (in the form of timesheets) that is not reliable, the Contractor has to find a way such as to make it reliable and that is done by taking the position: "Whilst the labour was wholly employed, productivity was adversely affected by (say) 50% by reason of the Employers failings."
That position is often supported by masses of calculations/spreadsheets as to programmed against actually employed resources (allegedly adjusted for variations), assorted graphs, histograms and the like, bus timetables (if useful) and the en vogue "measured-mile" analysis.
The problem is of course, the Contractor has already given (say) 50% away because the timesheets do not record that which is fact and now it has to attempt to prove Inefficiency allegedly caused by the Employer and based on presumptions, largely notional calculations and analyses that often do not stand up to scrutiny. The Contractor therefore has to find other ways to attempt to recover its unproven losses and which almost inevitably results in an imaginatively (and sometimes grossly) inflated claim.
The employer is then presented with an inflated claim that is only partially evidenced and has three main choices:
Rely on its belief that the Contractor can prove only a fraction (if anything at all) of what it is claiming (an essentially legal defence); or
Attempt to disprove the Contractor's case by submitting evidence of its own Ian essentially factual defence); or
Adopt a line of defence comprising both aspects of 1. and 2. above.
Given that, in my experience, an Employer would be almost recklessly brave to rely on 1. (or for that matter 2.) above alone, evidence is just as an essential part of an Employer's Defence as it is to a Contractor's Claim.
The conclusion has to be that any case is only as good as the evidence in support of it and that evidence has to go directly to the case brought and defended.
The final and major problem that remains to be resolved is that the parties to a dispute quite often do not know what evidences facts that go directly to the issue(s) in dispute and what is mere fiction.
It's all a matter of substantive proof and in that regard the parties may be well advised to seek professional assistance at an early stage.