Yes, this is completely normal and happens to nearly every language learner, especially with words encountered in natural reading or listening rather than structured study. Forgetting a word three or more times before it sticks is not a sign of poor memory; it is how your brain builds durable long-term recall through repeated, spaced exposure.
The key insight is that your current method of writing words down is a good start, but it lacks two critical elements: active retrieval and spaced repetition. Simply noting a word when you look it up is a passive act. To make it stick, you need to actively test yourself on the meaning after a delay, and then again at increasing intervals. This is the principle behind spaced repetition systems (SRS), which are far more efficient than traditional flashcards because they schedule reviews just before you would forget.
You mentioned finding flashcards boring and time-consuming when they pile up. The solution is not to abandon the idea entirely, but to optimize it. Instead of a physical deck or a basic digital list, use a digital app that automates spaced repetition. Many free or low-cost options exist. When you add a word, include a simple example sentence in the target language (the one you are learning) that shows the word in context. Avoid translations; use a definition or a visual cue. This makes each card a mini-contextual encounter, which is more engaging than a bare word-translation pair.
Another powerful technique is to create a personal connection. After looking up a word, immediately use it in a sentence about your own life, or associate it with a vivid mental image. For example, if you learn the word "stumble" (as in to trip), imagine yourself stumbling over a specific object in your room. This emotional or personal hook dramatically improves recall.
Finally, accept that some words will require many encounters. Aim for quality over quantity. Add no more than 5-10 new words per day, and focus on reviewing the ones that keep slipping. Over time, your brain will learn which words need more reinforcement. The frustration you feel is actually a sign of progress; your brain is actively trying to integrate new information. Keep going, and trust the process.
For Dutch specifically, focus on high-frequency words that appear in common phrases or idioms. This will give you more natural repetition from everyday exposure.