My Magento 2 Observer was called multiple times due to Plugins/Interceptors. This Observer will not be triggered by Plugins.

NotTriggeredByPluginsObserver.php

<?php

namespace Cmtickle\Sample\Observer;

use Magento\Framework\Event\Observer;

class NotTriggeredByPluginsObserver implements \Magento\Framework\Event\ObserverInterface
{
    const INTERCEPTOR_FUNCTION = 'Magento\Framework\Interception\{closure}';

    /**
     * @return bool
     */
    private function isTriggeredByPlugin()
    {
        $stackTrace = debug_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS);
        $callCount = count($stackTrace);
        for ($callPos = $callCount - 2 ; $callPos >= 1; $callPos--) {
            $calledByInterceptor = self::INTERCEPTOR_FUNCTION === $stackTrace[$callPos - 1]['function'] &&
                self::INTERCEPTOR_FUNCTION === $stackTrace[$callPos + 1]['function'];

            if ($calledByInterceptor) return true;
        }

        return false;
    }

    /**
     * @param Observer $observer
     * @return void
     */
    public function execute(\Magento\Framework\Event\Observer $observer)
    {
        if($this->isTriggeredByPlugin()) {
            return;
        }

        # Your code here.
    }
}