Simple things need be simple only in and of themselves, as instantly recognizable: "I know what that is," we say when we hear the definition. "The heart is deceitful above all things, and desperately wicked," says the King James Version, leaving no doubt in meaning, but offering us no clue as to what exactly this unconstrained, deceitful, wicked heart will do. By definition, it is undependable and unpredictable in the consequences of its actions.
Two such simple things are bluster and incompetence. My online dictionary says that bluster is "loud, arrogant speech, often full of empty threats." Incompetence is defined as an absence "of those qualities requisite for effective conduct or action." Well-intentioned and hard-working people become incompetent when they have bitten off more than they can chew, and also lack two indispensable qualities required for effective conduct or action—humility and honesty. People with those seek to minimize and limit the harm their incompetence has caused or furthered.
Bluster may be merely comic, as illustrated by Mr. Fawlty in the British television series FawltyTowers. The joke is on the blusterer, who brings ridicule upon himself.
When bluster and incompetence combine, it isn't funny anymore. Power is placed in the hands of blusterers who pledge themselves to tasks beyond their reach. They say they can finish a job if they are given $87 billion but who, three and a half years and hundreds of billions of dollars later, still haven't the finished the job—yet they expect more money still. Another example is crime-fighters running for office who have prosecuted innocent people, covered it up, and then bragged about their good record. There are teachers who put children in the wrong rather than admit to a mistake. There are executives who lie to their stockholders in order to keep prices up.
In each of those cases, incompetent blusterers may be lying to themselves as well as to others—no more than is to be expected if the Bible has it right about deceitful and desperately wicked hearts.